The development of gear shaving (also gear honing) started with the so-called parallel shaving, this is a method, in which the advance or movement of the workpiece relative to the tool occurs with the axis of the tool extending parallel to the workpiece axis. For the purpose of the chip removal, the tool is moved in strokes relative to the workpiece. One started then to direct the relative advance of the axis of the tool angularly with respect to the workpiece axis, through which the operating time could be shortened and wherein the tool is worn more evenly because of the crossed-axes point wandering alongside of the tool teeth. In this method, which in the technical language is called diagonal shaving, the tool is also moved in strokes relative to the workpiece. During a further development, the direction of the advance was then swung so far that it was directed at a right angle with respect to the workpiece axis. A chip removal radially with respect to the workpiece axis (depth feed motion) no longer took place. The operating time was extremely shortened in this method which is called, in the technical language, underpass-shaving. In all abovedescribed methods there occurs a change in the direction of rotation of workpiece and tool at the end of the advance. (Hurth-gear-shaving (1964)), Page 208 et seq.
Underpass shaving has led to a considerable reduction of the operating time, however, gears with an insufficient surface quality and with flank profile errors were produced. The latter were additionally worsened by being different on the right and left flank of the respective teeth. To reduce these deficiencies, one first varied the cutting speed and the advance speed, which was not sucessful. Then, during the course of a further development, a stepwise radial feed was introduced which, because of the time involved, was supposed to be avoided in particular by the underpass-shaving. Thus one fell back through the development of the underpass-method onto the diagonal method with stroke-like radial feed.
The basic purpose of the invention is to provide a method, which assures, on the one hand, the short operating time of the underpass-method, however, on the other hand, achieves a higher surface quality and tooth quality.
To attain this purpose, the inventors first examined the course of the chip removal during the advance, in particular by comparing the two sides of the workpiece teeth, namely during different advancing and cutting speeds, but this actually did not yet lead to any satisfactory result. Only an examination of the operations of the reciprocal action of flank and counterflank on the respective tooth side brought about the attainment of the set purpose.
The time period for the change in the direction of rotation exists inventively on the part of the advance path, on which chips are removed on both sides of the workpiece teeth. To determine the exact time period, one must note the geometry of the workpiece, the chip allowance, the workpiece width and the form of the elastic flattening, which in turn depends on the curvature radii of the tooth flanks, on the crossed-axes angle and contact pressure (see for this Hurth-gearing-shaving (1964) Page 220). The following tendency must be considered for the time period of the change in the direction of rotation. When the pitch diameter is large, the point of the change in the direction of rotation lies farther away from the point of the smallest axial distance (common normal line) of workpiece and tool than in the case of a small pitch diameter, similarly in the case of a large working tolerance. The exact point of the change in the direction of rotation is determined advantageously by operating tests.
Generally the method according to the invention is carried out changing the direction of rotation prior to reaching the smallest distance between axes. Only in cases of an exception is the direction of rotation supposed to change at the point of the smallest axial distance, however, the success of the invention can hereby be lost. In this connection the elastic flattening is again brought to mind. Optimum conditions are obtained by directing the advance at a right angle with respect to the axes of the workpiece or the tool. The advances must be varied under high quality requirements.
For high requirements concerning the quality of the toothing which is to be produced, it is of extreme importance to cause the return stroke to take place with reduced speed from the point of smallest distance between the axes to the point of approximate release of the tooth flanks. A reduction of the advance speed can exist from the start of the return stroke over the point of the smallest axial distance until the release of the tooth flanks from one another. Of a decisive influence is, however, the area from the point of the smallest axial distance to the release of the tooth flanks from one another. The type of this characteristic is connected with the elastic stresses which are stored during the working in the device and their release.
Of particular importance is the device for controlling the direction of rotation which is effective during the abovedescribed section of the advance. This device can consist substantially of cams and switches in the advance path or of a control roller or the like which runs synchronously with the advance or of a time relay which, starting out from a fix point of the advance, for example, the start of the same, causes after a predetermined time at a desired point of the advance the change of the direction of rotation. The device may also be a numerical or a different suited electric, hydraulic or pneumatic control.
In the case of high quality requirements, the speed (cutting speed) must also be changed dependent from the advance.
A tool for the method according to the invention is similar to the one for the known plunge-shaving method, however, differs inventively from same in that the curvatures in the longitudinal direction of the teeth do not cling to one another over the entire gear width.
The device for controlling any operations is not limited to the exemplarily mentioned types, but it is possible to use all suited mechanical, electric, hydraulic or pneumatic controls.
Further advantages and characteristics of the invention can be taken from the following description.